Merge tag 'pm-4.18-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull power management fix from Rafael Wysocki:
 "Fix a relatively old initialization issue in intel_pstate causing the
  pcc-cpufreq driver to be used instead of it on some HP Proliant
  systems.

  This turned into a functional regression during the 4.17 cycle,
  because pcc-cpufreq is a scalability disaster and that was amplified
  by the idle loop rework done at that time (Rafael Wysocki).

* tag 'pm-4.18-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  cpufreq: intel_pstate: Register when ACPI PCCH is present

drivers/cpufreq/intel_pstate.c

@@ -2394,6 +2394,18 @@ static bool __init intel_pstate_no_acpi_pss(void)
 	return true;
 }
 
+static bool __init intel_pstate_no_acpi_pcch(void)
+{
+	acpi_status status;
+	acpi_handle handle;
+
+	status = acpi_get_handle(NULL, "\\_SB", &handle);
+	if (ACPI_FAILURE(status))
+		return true;
+
+	return !acpi_has_method(handle, "PCCH");
+}
+
 static bool __init intel_pstate_has_acpi_ppc(void)
 {
 	int i;
@@ -2453,7 +2465,10 @@ static bool __init intel_pstate_platform_pwr_mgmt_exists(void)
 
 	switch (plat_info[idx].data) {
 	case PSS:
-		return intel_pstate_no_acpi_pss();
+		if (!intel_pstate_no_acpi_pss())
+			return false;
+
+		return intel_pstate_no_acpi_pcch();
 	case PPC:
 		return intel_pstate_has_acpi_ppc() && !force_load;
 	}

drivers/cpufreq/pcc-cpufreq.c

@@ -580,6 +580,10 @@ static int __init pcc_cpufreq_init(void)
 {
 	int ret;
 
+	/* Skip initialization if another cpufreq driver is there. */
+	if (cpufreq_get_current_driver())
+		return 0;
+
 	if (acpi_disabled)
 		return 0;